NEW ORLEANS — If you`re the typical American voter, the chances are 50-50 that you already know whether you`re going to vote for the Democrat or the Republican for president next year.

No insult intended, but if you do, you`re not very important in the long run. You`re important now, because you may help your party choose its nominee. After that, though, it`s the other folks who get all the attention.

Now, as for the rest of you. According to the surveys, you`re probably a Democrat, but not as fervent about it as your parents were, or even as fervent as you were 20 years ago, if you`re old enough. You`re also probably white, middle income, under 50, reasonably content, but worried.

``There`s no buoyancy out there,`` said pollster Jeffrey Gerrin. ``People are restless.``

Gerrin is a Democrat. But Republicans agree, at least to a point.

``We can`t rest on our laurels,`` said Frank Fahrenkopf, the chairman of the Republican National Committee, which met here last week. For all their loyalty to President Reagan, none of the Republican candidates is basing his campaign on the theme that ``it`s morning again in America.``

What you`re worried about, the pollsters say, is schools for your young children, health care for your aging parents and the future of the economy

--the specter, as pollster Stanley Greenberg puts it, that your children`s economic choices will be ``McDonald`s or the Navy.``

The statistical evidence about the decline of the middle class and falling real wages is confusing and ambiguous. But because you worry they may be right, you`re thinking about voting Democratic.

On the other hand, you still like Reagan, if not as much as you did a year ago. And while you like the Democrats on the issues--health care, schools, arms control, environment--you like the Republican themes--national strength, economic growth, low taxes.

And even Democrats admit that you have some worries about them. ``Doubts about Democrats center around defense and social issues,`` Greenberg said.

You also tend to fear that the Democrats will spend too much of your money. Or as expressed by one Democratic candidate, Sen. Joseph Biden, of Delaware, ``The folks don`t trust us on taxes.``

Still, most of the polls indicate that right now you`re likely to vote Democratic, in part because you think of yourself as a Democrat. Party affiliation isn`t what it used to be, say the pollsters and political scientists, but it`s still something.

But party identification is only one of several factors that will help you make your decision. The others are the issues, the candidates and the situation.

Notice that the word ``ideology`` is not in that list. This does not mean ideology isn`t important. It is, to some people. But you are not one of them. The real liberals and the real conservatives are in that 50 percent whose votes are not up for grabs.

One problem both parties have is that these true believers

--``politicized`` people in polysci-ese--tend to dominate the nomination process, making it easier for a conservative to win the Republican nomination and a liberal to win the Democratic line than for either to win the election. Another problem is that it is the politicized people who pay more attention, making it likely that if you are one of the people this exercise is about, you aren`t reading it, raising an interesting metaphysical question that will not be answered here.

So just because you`re thinking about voting Democratic doesn`t mean you have become a liberal. But then, you didn`t really become a conservative when you voted for Reagan, either, even if he convinced you to vote for other Republicans, too.

According to the surveys, it was the situation, Reagan`s performance, that won you over in 1984.

``It was the results,`` said politicial science Prof. Raymond Wolfinger of the University of California. ``People are not asking for the policies the Republicans are advocating.``

In other words, when things are all right and getting better, you tend to like the party in power. When they aren`t, as in 1980, you don`t.

Actually, it might be more accurate to say that you like it when things seem to be getting better. In 1980, when Reagan asked that now-famous question --``Are you better off now than you were four years ago?``--the real answer, according to the statistics, was ``yes.`` Real disposable income rose by 11.6 percent during Jimmy Carter`s presidency.

But it had hardly gone up at all in Carter`s last two years. In Reagan`s first term, the increase was 14 percent, not that much better than Carter`s. In the last two years of Reagan`s first term, though, the increase was a respectable 5.8 percent.

In politics, as on Broadway, the key is, ``What have you done for me lately?``